A basic service set (BSS) is a basic component of a wireless local area network (WLAN). Stations (STA), which are located within a specific coverage area and have certain association, form a BSS. A most basic form of the association is that the stations directly communicate with each other in a self-organizing network, which is referred to as an independent basic service set (Independent BSS, IBSS).
In a more common situation, an STA associates with a central station, which is especially responsible for managing a BSS; the central station is referred to as an access point (AP). A BBS established around an AP is referred to as a BSS with infrastructure. BBSs with infrastructure may be connected to each other by APs thereof through a distributed system (DS), so as to form an extended BBS (ESS).
Transmission on a wireless medium is prone to errors. For example, for data (DATA) transmission, a low delay retransmission mechanism at a link level is beneficial. This mechanism allows those frames, which are not correctly demodulated by a receiver, to be retransmitted. A basic method for implementing this point is to enable a station correctly receiving a data frame to send a timely acknowledgement in a format of an acknowledgement frame (ACK, Acknowledgement). If a station sending the data frame does not receive the ACK frame, the station sending the data frame assumes that the data frame is not correctly received and may retransmit the frame. For interaction between frames of other types, for example, for a Confirm To send (CTS) frame of a Request To Send (RTS,) frame, the mechanism of the acknowledgement frame may also be adopted similarly.
In an 802.11 network, data (DATA) includes a quality of service (QoS) control field, and this field includes an acknowledgement policy field. Currently, there are several acknowledgement policies as follows:
policy 1: normal acknowledgement or implicit block acknowledgement;
policy 2: non-acknowledgement;
policy 3: non-explicit acknowledgement or scheduled acknowledgement under PSMP (power save multi-poll); and
policy 4: block acknowledgement.
In the first acknowledgement policy (the policy 1), for QoS data in a non-aggregated packet, a receiving end is specified to return an ACK frame. The ACK frame needs to be returned immediately, and a time interval between the returning of the ACK frame and a time point at which a sending end finishes dispatching data last data is a short inter-frame space (SIFS). An MAC (Media Access Control, media access control) layer portion of the ACK frame may also be referred to as a PLCP (Physical Layer Convergence Procedure) service data unit (PSDU, PLCP service data unit) or a data unit, and includes a frame control field, a duration field, a receiver address (RA) field, and a frame check sequence (FCS) used for demodulation and checking.
In a situation of a low rate, for example, a low-order modulation manner like BPSK (Binary Phase Shift Keying), or in a situation of a low coding rate, for example, ½ coding, an overhead taken for transmitting the MAC layer portion is large. Taking 802.11ac as an example, at a rate of 6 Mbps with a bandwidth of 20 M, each OFDM (Orthogonal Frequency Division Multiplexing) symbol may transmit three bytes. In this way, the MAC layer portion of the ACK has a total of fourteen bytes and needs to take five OFDM symbols. Besides, a preamble portion (preamble) of a physical layer has a total of six OFDM symbols. In this way, the overhead for the MAC layer portion amounts to 45% of a whole, which reduces the interaction efficiency of the acknowledgement frame.